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Techies....

Here's some thoughts from a PCB fabricator....

First of all, great input from everyone. As usual Dwight nailed it.
Eventually all vias will fail under the right conditions...

My group acquired an IST tester earlier this from PWB Corp,
(www.pwbcorp.com) and it was amazing how quickly we could
pin point the trouble spots in our via process, i.e. laminate, oxide, drill,
desmear, (etchback when required), electroless, copper plate, etc.

The three most significant impacts to via reliability were drill (hole wall
quality),
laminate (#1), and copper thickness (#2). We could double the life cycles
of our thermal cycles by changing the laminate or increasing the copper
thickness.

There is one subject, I did not see discussed... BGA rework.... Typically
your BGA sites have the highest density of vias per square inch. Many of
our clients allow up to 5 rework cycles. The vast majority of via failures
on our
products are typically under BGAs... The Z axis expansion of the laminate
after several thermal excursions is remarkable.

Jim
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dwight Mattix
Sent: Friday, December 06, 2002 11:04 AM
To: [log in to unmask]
Subject: Re: [TN] Via Cracking

Hole wall roughness is also a major determinant of number of cycles to
failure. The rougher the hole -- the more stress risers for cracks to start
propagating from. That's why I seen many holes with thinner copper but
clean drilling outlast thicker copper holes with rougher drilling.

All in all, it's not so much a question of whether a holewall will crack
after thermal cycling. It's a question of when it'll crack or how cycles
it'll take to start cracking when thermal cycled (wearout point on the
classic reliability bathtub curve).

Soon or later we all die and sooner or later hole copper will start
cracking if it sees enough temp cycling.

Dwight

At 08:15 PM 12/5/2002 -0800, Roger Mouton wrote:

Werner,

Your comments are well taken. I think you know what I was getting at
Throughout the mid 80's I saw time and again where thin deposits cracked
and
thicker ones held together. And thanks for the clarification on
elongation
testing.

Best,
Roger Mouton

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